A poultice, cooling sheet, or like skin patch is produced by applying a gel-like plaster, which has been prepared by adding various medicaments, water, or other ingredients to a composition containing a water-soluble polymer, to the surface of a nonwoven fabric or like support, and curing and aging the composition, thereby forming the plaster layer on the support. Examples of water-soluble polymers that may be added to such a composition include poly(meth)acrylic polymers, such as poly(meth)acrylic acid or a salt thereof.
A composition for forming a plaster layer that contains a water-soluble polymer and that is used for a skin patch is required to have sufficient adhesiveness to the skin, elasticity for application to a bending part, and other properties. It is also required to have various other properties adopted to the skin patch production process.
A typical process for producing a poultice or cooling sheet comprises the steps of preparing a gel-like plaster by mixing various additive ingredients to a composition containing a water-soluble polymer, applying the gel-like plaster to a nonwoven fabric or like support, covering the surface thereof with a polyethylene film or like liner, cutting and packing the result, and then curing and aging the composition in the pack.
In such a method, when a gel-like plaster is prepared from the water-soluble polymer composition, aluminum or a like polyvalent metal compound is added to the water-soluble polymer composition as a cross linking agent. If the water-soluble polymer easily reacts with the polyvalent metal compound and the curing speed is too fast, gelation proceeds during the application of the water-soluble polymer to the support, making it difficult to apply it to the support. Therefore, in order to control the reaction speed between the water-soluble polymer and the polyvalent metal compound, a method is employed wherein disodium ethylenediaminetetraacetate is also added as a gelation rate retarding agent when adding the polyvalent metal compound (Patent Literature 1).